1. Field of the Invention
The present invention relates to a process for preparing a high performance composite carbon fiber reinforced carbonaceous material (hereinafter referred to as "CFRC") which is compositely reinforced with carbon fibers.
2. Prior Art
CFRC has been used, for instance, in leading edges of high speed aircraft, nozzles or nose cones of rockets, disk rotors, and pads for friction in brakes, etc., because it is light, highly heat-resistant, characterized by high strength at a high temperature and is excellent in abrasion resistance as material adapted for use in the parts exposed to high temperatures or generating severe friction.
Heretofore, CFRC has been prepared mainly by a liquid phase impregnation process and a chemical vacuum deposition process (hereinafter referred to as "CVD process"). In the liquid phase impregnation process of preparing CFRC, prepregs of woven fabrics of carbon fibers impregnated with a resin such as phenol resin, furan resin, epoxy resin, urea resin, etc., are laminated as a matrix and molded under heat and pressure, and after carbonization, they are further graphitized by heating to a temperature close to 3000.degree. C. However, this process appeared to be unsatisfactory in that the structure of the product obtained thereby becomes loose due to gases generated as a result of thermal decomposition of the resin in the course of the carbonization and graphitization. For the foregoing reason, in order to obtain a complete product, the step, wherein the product once subjected to the graphitization treatment is impregnated with pitch under pressure and again subjected to the carbonization and graphitization treatments, has been repeated many times over until the desired density of the product is attained. The repeated carbonization and graphitization treatments required considerable labor, energy, and time. In addition to the above, besides the gases which are generated by the thermal decomposition of the resin in the course of the carbonization of the prepreg product of the carbon fibers impregnated with a resin in such a liquid phase impregnation process, crack formation and interlayer separation are caused owing to the thermal stress strain generated in the product as a result of the difference between the volume contraction of the resin accompanying the carbonization and the coefficient of thermal expansion of the carbon fibers, which lowers the shearing strength or damages the product greatly, so that the production yield has been considerably aggravated.
Further, in this liquid phase impregnation process one cannot take advantage of the mesophase pitch, the molecular weight of which has been made so high that it does not dissolve in solvent.
The CVD process is a process in which a gaseous organic compound is brought in contact with the carbon fiber base material heated to a high temperature under a diminished pressure so as to deposit carbon atoms on the base material. It has been noted in the CVD process that the state of carbon deposition becomes uneven due to lack of uniformity of the heat conductivity of the carbon fiber base material, or a thick molded product with a differing structure between the internal portion and the surface portion, characteristics which are undesirable. Moreover, since the steps required are complicated and time-consuming in both the liquid phase impregnation process and the CVD process, it has been one of the reasons that it is expensive to make CFRC.
On the other hand, anyone would be able to think of the idea that if, as the matrix, use is made of a fine powder or bulk mesophase of raw coke which was preliminarily heat-treated so as to increase the yield in the residual carbon in place of the liquid matrix, fewer components will volatilize in the carbonization, rendering it possible that the baking is achieved in a short period of time with a decreased volume contraction, so that the stress strain in the molded body also decreases and the defects such as the crack formation, interlayer separation, etc., are eliminated and thus the most desired process for preparation of CFRC can be realized. Nevertheless, to tell the truth, it is very difficult to uniformly and, moreover, sufficiently adhesively coat the surfaces of the base material carbon fibers with a fine powder or bulk mesophase of raw coke; and therefore, it is the present state that good CFRC has not as yet been produced.
In view of the above described defects, the invention of this application was accomplished, and its object is to provide a carbonaceous material which can exhibit the ideal composite effect in preventing the crack formation, interlayer separation between the laminated layers of the base material during the manufacturing course of the carbonaceous material reinforced with carbon fibers or CFRC.